FXUS66 KMTR 261755
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
955 AM PST SAT DEC 26 2009

.DISCUSSION...AS OF 9:30 AM PST SATURDAY...NO FORECAST UPDATES
EXPECTED THIS MORNING. MAIN FORECAST FOCUS WILL BE ON RAIN CHANCES
OVER THE NEXT 36 HOURS.

KMUX RADAR IS SHOWING INCREASING RADAR RETURNS OFF THE COAST AT THIS
HOUR AS ELONGATED BOUNDARY APPROACHES THE REGION AND BUMPS INTO THE
WEST COAST RIDGE. 12Z OAKLAND AND VANDENBERG SOUNDINGS SHOW THE MID-
LEVELS ARE STILL PRETTY DRY SO SOME MOISTENING WILL NEED TO TAKE
PLACE BEFORE THE COLUMN SATURATES AND MOISTURE REACHES THE GROUND.
CURRENT FORECAST INTRODUCES RAIN CHANCES THIS AFTERNOON WITH BETTER
CHANCES BY THIS EVENING. THAT STILL LOOKS GOOD WITH EXPECTATION OF
MOST COASTAL LOCATIONS TO SEE LIGHT RAIN BY 00Z AND CONTINUING
THROUGH THE EVENING. LIGHT RAIN BAND WILL BE ORIENTATED PARALLEL TO
THE COAST SO LIGHT RAIN SHOULD DEVELOP AT ALL COASTAL LOCATIONS FROM
SONOMA SOUTHWARD TO MONTEREY AROUND THE SAME TIME AND THEN MARCH
INLAND THROUGH THE EVENING AND OVERNIGHT HOURS. QPF TOTALS EXPECTED
TO BE LIGHT WITH A FEW TENTHS TO A QUARTER INCH MOST LOCALES AND
PERHAPS 0.50-0.75 FOR SOME OF THE WETTEST COASTAL HILLS...OROGRAPHICS
DONT LOOK TOO GOOD. LATEST 12Z NAM AND GFS RUNS SUGGEST MOST OF THE
PRECIP TO FALL TONIGHT THROUGH EARLY SUNDAY MORNING. SHOWERS WILL
STAY IN THE FORECAST THROUGH SUNDAY AFTERNOON AND EVENING BUT THINK
THE BULK OF STEADY RAINS WILL BE DONE BY 18Z SUNDAY.

OVERALL LARGE SCALE PATTERN IS STILL CHARACTERIZED BY A HUGE TROUGH
OVER THE CENTRAL CONUS. CLOSER TO HOME THERE ARE SEVERAL PIECES OF
ENERGY OVER THE EASTERN PACIFIC. MODEL DETAILS ON ALL OF THIS ARE
MURKY AS JET ENERGY OVER THE EASTERN PACIFIC IS SPLIT AND
DIFFUSIVE. BEST ESTIMATE AT THIS TIME IS THAT MUCH OF MONDAY AND
TUESDAY LOOK DRY WITH NEXT CHANCE OF ORGANIZED RAIN LATE TUESDAY
NIGHT INTO WEDS...WITH BEST CHANCE FOCUSED ACROSS THE NORTH BAY.
WILL FOCUS MORE ON THE LONG RANGE FORECAST WITH THE AFTERNOON PACKAGE
BUT AS ALLUDED TO BY THE OVERNIGHT FORECASTER THE WEEK LOOKS SOMEWHAT
UNSETTLED BUT NO WASH-OUTS EXPECTED. BEST RAIN CHANCES LOOK TO BE IN
THE NORTH BAY WHICH IS WHERE THE RAIN IS NEEDED MOST WITH SANTA ROSA
ONLY AT 69% OF NORMAL AND UKIAH AT 55% OF NORMAL.  THE USUALLY WET
SPOTS OF FAR NORTHERN CALIFORNIA INCLUDING CRESCENT CITY REMAIN
WELL BELOW SEASONAL NORMS FOR THE TIME BEING. ONE MONTH OF THE RAINY
SEASON WILL SOON BE BEHIND US FOR BUILDING UP RESERVOIR CAPACITY.

&&

.AVIATION...AS OF 9:55 AM SATURDAY...RADAR AND SATELLITE IMAGERY ARE
INDICATING A COLD FRONT APPROACHING THE COAST. AHEAD OF THE COLD
FRONT EXPECT WINDS OUT OF THE SOUTH. ATMOSPHERE ON LATEST KOAK
SOUNDING SHOWS A DEEP DRY LAYER WHICH WILL TAKE SOME TIME TO
SATURATE BEFORE PRECIPITATION BEGINS TO REACH THE GROUND.

VICINITY OF KSFO...VFR EXPECTED THROUGH THIS AFTERNOON WITH CEILINGS
SLOWLY FALLING. LOW VFR CIGS AROUND 3500 FEET WITH A LIGHT SHOWER
BY 0200 UTC. SHOWERS WILL END AT THE TERMINAL BY 1100 UTC SOME
SHOWERS WILL LINGER AROUND THE AREA THROUGH TOMORROW.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR EXPECTED THROUGH THIS EVENING WITH
CEILINGS SLOWLY FALLING THROUGHOUT THE DAY. LOW VFR CIGS AROUND 3000
FEET WITH A LIGHT SHOWER BY 0200 UTC. SHOWERS WILL END AT THE
TERMINAL BY 1100 UTC SOME SHOWERS WILL LINGER AROUND THE AREA THROUGH
TOMORROW.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
   .TDY...SCA...PT ARENA TO PIGEON PT 10-60 NM
       ...SCA...PT ARENA TO PT REYES 0-10 NM STARTING THIS AFTERNOON
       ...SCA...FOR ROUGH BAR BEGINNING AT 4 PM.

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: LARRY

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO